GENERAL METABOLISM. 637 



requirement is met with nitrogen-free food. It is then impossible to pre- 

 vent the animal from losing weight even when far more fat and carbo- 

 hydrate are fed to it than corresponds to the calories required when the 

 dog was in metabolic equilibrium with albumin present in its food. 

 As soon as the albumin is wanting in the food supply, starvation 

 metabolism begins, i.e., body albumin begins to be decomposed. It is 

 true that the animal lives a few days longer than if it were absolutely 

 starving on account of lack of all food, but it will gradually die as a result 

 of albumin starvation. The decomposition of albumin shows a peculiar 

 behavior when varying amounts of albumin are present in the food. The 

 more albumin the animal eats, the more there is decomposed. To be sure, 

 by greatly increasing the amount of albumin it is possible for the organism 

 to store away material, but usually not in the form of albumin itself. The 

 cells of the body evidently strive to keep the albumin content of the organ- 

 ism at a constant level. It is possible to bring an animal into so-called 

 nitrogen equilibrium with different amounts of albumin. Equilibrium is 

 reached when the organism experimented upon eliminates the same amount 

 of nitrogen that it receives. This relation is most apparent if instead of 

 estimating the amount of nitrogen eliminated during a single day, a period 

 of several days is studied. 



The fact that an increase in the albumin income also causes an increase 

 in the total metabolism apparently helps to enable us to decide whether 

 the cell-material, or protoplasm, itself takes part directly in the decompo- 

 sitions and combustions, or whether we have to distinguish sharply between 

 the cell-nutriment and the cell-building-stones. Here we meet with the 

 most important problem of metabolism. It is quite generally assumed that 

 in animal combustions it is chiefly the albumin in the nutriment, also 

 designated as circulating albumin, which is consumed, while the living 

 protoplasm is only drawn upon for the outgo when there is a deficiency in 

 the supply of albumin. There are a number of observations which support 

 this assumption. Above all, it is remarkable how quickly the albumin is 

 oxidized after its introduction into the organism. Within a few hours the 

 total amount of nitrogen reappears in the urine. It is hardly absorbed 

 before its elimination begins. Although the presence of -fat and carbo- 

 hydrate in the food somewhat diminishes the decomposition of albumin, 

 still on the whole the decomposition of the albumin is about the same as 

 with a purely meat diet. The fact that the extent of albumin decomposi- 

 tion is, within wide limits, independent of the albumin content of the body 

 itself, has also been cited as supporting the above conception. The 

 assumption that the tissue-cells of the fully developed animal organism 

 are in a relatively stable condition, and work essentially by means of the 

 energy obtained from the food, is an attractive one. According to this, 

 the cell takes up from the blood, or the plasma, the substances which it 



